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L-L Chen, JK B Johansson, RR Hodges, D Zoukhri, DA Dartt; Effect of the EGF Family of Growth Factors on Protein Secretion and MAPK Activation in Rat Lacrimal Gland . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3147.
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Purpose:To determine which of the ErbB receptors (ErbB1-4) are linked to stimulation of protein secretion and activation of p44/p42 mitogen-activated protein kinase (MAPK) in rat lacrimal gland. Methods:Both exorbital lacrimal glands were removed from male Sprague-Dawley rats. The lacrimal glands were fixed, cryopreserved, frozen, and sectioned (6 µm). Sections were processed by standard immunofluorescence techniques using antibodies against ErbB receptor family subtypes. Acini were isolated by collagenase digestion, and incubated with members of the EGF family of growth factors EGF, TGF-α, heregulin, and HB-EGF at 10-7M or the cholinergic agonist carbachol (10-4M), a known stimulus, either for 20 min (secretion) or 10 min (MAPK activation). Peroxidase secretion, an index of protein secretion in lacrimal gland, was measured in both the supernatant and the homogenate of acini using a fluorescence assay kit. For MAPK activation, Western blot analysis using antibodies specific to phosphorylated MAPK or total MAPK was performed on the homogenate of acini, and immunoreactive bands were quantified. Results:All four ErbB receptors were present in basolateral membranes of acinar cells. Carbachol caused a 3.0 fold increase in secretion. The EGF family of growth factors stimulated secretion with the following order of efficacy: heregulin≷HB-EGF≷TGF-α≷EGF. Carbachol caused a 4.0 fold increase in MAPK activity. The EGF family of growth factors activated MAPK with the following order of efficacy: heregulin≷TGF-α≷EGF≷HB-EGF. Conclusion:We conclude that all four ErbB receptor subtypes are present in rat lacrimal gland, and could form homo- and heterodimers when activated. Heregulin, which binds to ErbB3 and -4, is more effective than HB-EGF, which binds to ErbB1 and -4, and EGF and TGF-α which bind to only ErbB1 in stimulating peroxidase secretion and MAPK activity. In addition, stimulation of secretion and activation of MAPK by the EGF family of growth factors is not correlated.
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